1. Field of the Invention
The present invention relates to a steady rest for centering a rotationally symmetrical workpiece in a space.
2. Description of the Prior Art
Steady rests of this kind have been used for decades for supporting rotationally symmetrical workpieces on machines tools. In particular with heavy and long rotationally symmetrical workpieces, it is necessary to secure them centrally in the space by means of one or more steady rests spaced apart from one another in order to prevent the bowing of the workpiece. The workpieces undergo bowing under their own weight, especially when they are rotating for machining involving metal cutting.
In the course of a plurality of machining steps, furthermore, additional machining forces are created which act on the workpieces and by means of which the central positioning of the workpiece can be changed. The steady rests of prior art are therefore intended to prevent the machining forces which act on the workpieces from giving rise to positional changes of this kind.
Machining involving metal cutting reduces the weight of the workpieces, as a result of which there is often also a change in position with the effect that the steady rests have to be reopened after a particular reduction in the weight of the workpieces in order to position the workpieces in the space so that the lengthways axis of the clamped workpiece runs along a straight line without deviating from a central axis.
A steady rest with an internal adjustment device for the central axis of the workpieces is disclosed in EP 0 554 506 B1. In order to achieve this, it is necessary for two outer steady rest arms to be moved differently in relation to one another in order to achieve the vertical alignment of the workpiece. Horizontal centering of the workpiece is performed jointly with all three steady rest arms, which come into working contact with the workpiece simultaneously or at different times from one another.
EP 0 554 506 B1 proposes an adjustment device for vertical and horizontal alignment of steady rest arms which has an extremely complex design.
It has proven to be a disadvantage of an adjustment device of this kind that it has to be opened in order to centre the workpiece. Following this, the stop points of the three steady rest arms must be changed depending on the necessary positional shift of the workpiece in space.
After this, the three steady rest arms grip the workpiece again and hold it.
Although this state of the art has proven effective for adjusting the feed movement of the steady rest arms, it is however necessary to open the steady rest arms with the effect that the clamping forces of the steady rest no longer act on the workpiece and this means that, in particular with heavy workpieces, there is a significant shift of position.